Agent for medicamentous treatment of acute and chronic pain

ABSTRACT

The invention relates to an agent for the medicamentous treatment of acute and chronic pain, in particular of allodynia and hyperalgesia. Fields of application of the invention are medice and the pharmaceutical industry. A new pharmaceutical composition for the treatment of acute and/or chronic pain, in particular allodynia and hyperalgesiais provided, the pharmaceutical composition comprising calcium channel blockers which are suitable for blocking voltage-dependent calcium channels, in particular of the T-type, more preferably the CaV3.2 channel and/or of the L-type. Mibefradil and dihydropyridines can, for instance, be used as calcium channel blockers.

The invention relates to an agent for medicamentous treatment of acuteand chronic pain, in particular of allodynia and hyperalgesia.

This invention can be applied in the fields of medicine andpharmaceutical industry.

Mechanical stimuli of different subjective sensation are perceivedthrough the skin, which is the largest sense organ in humans. Theperception of sensation ranges from soft contact, pressure and tickle toperceptions of pain due to strong mechanical impact.

Pain conditions that are triggered by a stimulus that, under normalconditions, does not cause any pain, are called allodynic. Prominentexamples thereof are a hypersensitivity of the skin due to a sunburn, aninflammation or a trauma. In order to distinguish it from hyperalgesia,it is important to note that allodynia is always connected with a changein the sensory modality. In other words, in the case of allodynia, itis, for instance, no longer possible to differentiate between thesensation modalities of a “soft touch” and “pain”, or, in other words,that a stimulus which is normally not painful causes pain. This meansthat there is a loss in the specificity of the sensory modalities. Incontrast, in the case of hyperalgesia, the quality of the sensorysensation has not changed. A touch is still perceived as a touch andpain is still perceived as pain. One, however, is more sensitive andquantitatively feels a more intensive touch or pain. The transition fromallodynia to hyperalgesia, however, is mostly gradual. It is at presentassumed that both the peripheral and the central sensitisation of thepain system contribute to the two pathological conditions (Julius D.Basbaum A I. (2001) Molecular mechanisms of nociception. Nature 2001413(6852):203-10; Textbook of Pain, (1999) ed. Wall P D and Melzack R.Philadelphia, Pa., W B Saunders, ISBN 0-443-06252-8).

Neuropathic pain, such as hyperalgesia and allodynia both occur assymptoms of many different and varied diseases and injuries(Epidemiology of Pain (1999), IASP Press, Editors: Ian K. Crombie, PeterR. Croft, Steven J. Linton, Linda LeResche, Michael von Korffm, ISBN0-931092-25-6). Examples thereof include syndromes such as rheumatoidarthritis, cancer pain, sport injuries, chronic and acute back pain,herpes zoster and post-surgical pain requiring intensive treatment. Thetreatment of neuropathic pain is often very difficult because of themultiple underlying mechanisms that are poorly understood. Any novelanalgetic target has a great therapeutic potential.

Allodynia is a pathological condition in which the person perceives softmechanical stimuli on the skin as pain, which, under normal conditions,are merely perceived as a soft contact of tickling. This is probably dueto a change in the connections in the spinal cord.

The different stimuli are registered by the endings of sensory neuronsthat are present in the spinal ganglion and the peripheral terminationsof which extend to the ends of the extremities.

Due to the requirements as to the processing of different mechanicalstimuli, this group of neurons has a very heterogeneous population. Theydiffer from each other in terms of the conduction velocity of theiraxons, the cell size, the threshold for mechanical generation ofstimulation and their adaptation behaviour:

-   1. A-β fibres (more than 10 m/s): slowly adapting SA fibres and    rapidly-adapting RA fibres (both tactile receptors)-   2. A-delta fibres (1-10 m/s): AM fibres (nociceptor) and D-hair    mechanoreceptors (highly sensitive tactile receptors)-   3. C-fibres (under 1 m/s) (nociceptors) Johnson (Kenneth O. Johnson,    2001, The roles and functions of cutaneous mechanoreceptors, Current    opinion in neurobiology, 11; 455-461, for mouse: Koltzenburg M,    Stucky C L, Lewin G R. Receptive properties of mouse sensory neurons    innervating hairy skin. J Neurophysiol. 1997 October; 78(4):1841-50)    summarises the cutaneous mechanoreceptors in humans.

Currently, two classes of pharmaceuticals are used for treatingallodynia and hyperalgesia, namely the class of non-steroidalanti-inflammatory drugs (NSAID) (such as indomethacin and aspirin) andthe opiates. The latter have an effect on the central nervous system andthey can only be applied to a limited extent due to the knownside-effects such as dependency and tolerance. The NSAIDs are effectivein the periphery and are therefore safer and more effective in manycases.

In chronic conditions such as rheumatoid arthritis, however, NSAIDs havenot turned out to be effective so that further targets for nociceptivetreatment have to be found. In this way, on the one hand, it would bepossible to develop agents that are more effective than the NSAIDs or,on the other hand, these classes of pharmaceuticals could besupplemented due to their different mode of activity and they couldmutually potentate their analgesic effect.

Thus, the technical problem underlying the invention is to develop a newagent for the medicamentous treatment of acute and chronic pain, inparticular of allodynia and hyperalgesia.

This technical problem is solved according to the claims.

According to the present invention, it was surprisingly found thatvoltage-dependent calcium channels are involved in the transduction ofmechanical stimuli by nociceptive/non-nociceptive neurons. As aconsequence, a blockade of the mechanical sensitivity of the skin bymeans of calcium channel blockers such as mibefradil or adihydropyridine derivative is the basis of the invention and thus offersa totally new treatment of pain such as allodynia and hyperalgesia.

A new pharmaceutical composition for the treatment of acute and/orchronic pain, in particular allodynia and hyperalgesia is provided for,comprising calcium channel blockers which are suitable for blockingvoltage-dependent calcium channels, in particular of the T-type, mostpreferably the CaV3.2 channel, and/or of the L-type. Mibefradil anddihydopyridine are preferred calcium channel blockers to be used inaccordance with the present invention.

Further calcium channel blockers including T-type channel blockers areknown in the art. Such substances which can be used in accordance withthe present invention include 1,4-dihydropyridine derivatives asdisclosed in WO98/31680, EP0164588 and EP0158211, succinimidederivatives like methylphenylsuccinimide, diphenylmethylpiperazinederivatives like7-[[4-[bis(4-fluorophenyl)-methyl]-1-piperazinyl]methyl]-2-[(2-hydroxyethyl)amino]4-(1-methylethyl)-2,4,6-cycloheptatrien-1-one (U92032; Pharmaciaand Upjohn), flunarizine, efonidipine, pimozide, zonisamide, depacon,amiloride and/or valproic acid.

The agent of the invention can, amongst others, be used in the treatmentof pain associated with rheumatoid arthritis, the formation and growthof tumours, injuries, back pain, herpes zoster and post-surgical pain.

The agent can be applied in local, oral, parenteral, inhalative orintranasal form, in any pharmaceutically acceptable form. In accordancewith a preferred embodiment of the invention, the calcium channelblocker is mibefradil (see FIG. 3), its pharmaceutically acceptableanalogues, salts and esters or dihydropyridines, such as diazepin, aswell as their pharmaceutically acceptable analogues (see FIG. 4). Inanother embodiment of the invention, for extending the possibilities oftherapy, ointments, gels or cremes and solutions or suspensions are usedas local forms of application. The pharmaceutical composition of theinvention can furthermore be included into a tape or can be applied inform of a spray, in particular a nasal spray.

Another advantage of the invention is that it can be applied for thesystemic treatment of pain. For extending the possibilities of therapy,tablets, capsules, coated tables, granulates, effervescent tablets,juice, syrup, suspensions or solutions can be used as oral forms ofapplication. In this case, the drug form used is formed of biologicallyutilizable or biodegradable substances, wherein the biological materialsare proteins or proteides, lipids or lipoids, carbohydrates orpolysaccharides or mixtures of several of such materials.

For extending the possibilities of therapy, in addition, to thepharmaceutical composition of the invention, at least one otheranalgetic, preferably of the NSAID class can be used. In this way, it ispossible to supplement the different biophases and to enhance theanalgetic effect.

Preferably, the concentration of mibefradil is between 1 and 10 μM, morepreferably 3 to 7 and most preferably 5 μM.

EXAMPLES

The invention described is now explained in more detail by way of thefollowing examples. The person skilled in the art can take various otherembodiments from the present description. Attention, however, is drawnto the fact that the examples and the description are merely intended toexplain and not to limit the invention.

Analysis of the occurrence and influence of voltage-dependent calciumchannels in D-hair mechanoreceptors

With regard to the research of pain, amongst the various kinds ofmechanoreceptors, in particular the so-called D-hair mechanoreceptorswhich are an excellent example of tactile receptors thanks to their highsensitivity. Stucky et al. found that in mice which lacked the gene forthe neurotrophin NT-4 a loss of D-hair mechanoreceptors occurs (Stucky CL, DeChiara T, Lindsay R M, Yancopoulos G D, Koltzenburg M.,Neutrotrophin 4 is required for the survival of a subclass of hairfollicle receptors. J. Neurosci. 1998 Sep. 1; 18(17):7040-6). In thepresent invention, these mice were used for the detection of genes whichare specifically expressed in D-hair and could therefore be importantfor their function. For this purpose, the gene expression of WT and NT-4ko (knock-out) mice were analysed in a comparison to detect genes thatwere under-regulated in NT-4 mice. As, with regard to the skin sensorysystem, the only difference between WT and NT-4 ko mice is the loss ofD-hair, these under-regulated genes were potential candidates for D-hairspecific genes. A combination of gene chip analysis and DNA subtractionmethods were used for expression studies. A combined analysis of thegene chip expression data and the DNA subtraction data resulted in 29genes which are most probably under-regulated in NT-4 ko mice. Fordetecting genes which are specifically expressed in a subtype of thespinal neurons, their expression pattern in the spinal ganglion wasanalysed. For this purpose, in-situ hybridisations with Dig labelledcRNA were carried out. D-hair specific genes should have been expressedin medium-size neurons and under-regulated in NT-4 ko mice.

All genes were expressed in a neuronal manner. Two genes fulfilled theabove-mentioned criteria for D-hair specificity. These were the genesTrkB and T-type calcium channel CaV3.2. (FIGS. 1 and 2)

TrkB ist the cellular receptor of NT-4 and BDNF and therefore anunder-regulation of TrkB in NT-4 mice could be expected and confirmedthe usefulness of the present experimental approach. The findings,however, that CaV3.2 is specifically expressed in D-hairmechanoreceptors is new and surprising as it has so far been unknownthat calcium channels are involved in mechanosensation.

Although T-type calcium currents have already been identified in theeighties by means of electrophysiological studies with chick sensoryneurons (Fox A P, Nowycky M C, Tsine R W, Kinetic and pharmacologicalproperties distinguishing three types of calcium currents in chicksensory neurons. J. Physiol. 1987 December; 394:149-72), the genes werecloned only recently. The T-type subtype CaV3.2 consists of 2042 aminoacids and was originally cloned in heart (therefore, its alternativename alpha1H) (Cribbs L L, Lee J H, Yang J, Satin J, Zhang Y, Daud A,Barclay J, Williamson M P, Fox M, Rees M, Perez-Reyes E. Cloning andcharacterization of alpha1H from human heart, a member of the T-typeCa2+ channel gene family. Circ. Res. 1998 Jul. 13; 83(1):103-9), but waslater on also detected in kidney and liver, and, to a smaller extent,also in brain. The expression studies underlying the present inventionshowed that CaV3.2 is expressed very specifically in medium-size spinalganglion cells. In the spinal ganglion, there are two kinds ofmedium-size neurons, the AM- and D-hair mechanoreceptors. Due to thefindings obtained by the present invention, i.e. that, parallel to theloss of D-hair, also CaV3.2 positive neurons disappear in NT-4 ko mice,it is obvious that CaV3.2 is specifically expressed in D-hair.

The logical question was which role said calcium channel plays in D-hairmechanoreceptors and whether it is indispensable for their function. Forthese studies, two known calcium channel blockers, i.e. mibefradil andnickel, were used (Martin R L, Lee J H, Cribbs L L, Perez-Reyes E, HanckD A, Mibefradil block of cloned T-type calcium channels. J. PharmacolExp Ther. 2000 October; 295(1):302-8 (Lee J H, Gomora J C, Cribbs L L,Perez-Reyes E. Nickel block of three cloned T-type calcium channels: lowconcentrations selectively block alpha1H. Biophys J. 1999 December;77(6):3034-42). Mibefradil (see FIG. 3) is a non-dihydropyridine calciumchannel antagonist that has a relatively high selectivity for T-typecalcium channels. Until a few years ago, mibefradil was used for thealternative treatment of hypertension and angina pectoris (Frishman W H,Mibefradil: A New selective T-Channel Calcium Antagonist forHypertension and Angina Pectoris. J Cardiovasc Pharmacol Ther. 1997October; 2(4):321-330) (Brogden R N, Markham A.: Mibefradil. A review ofits pharmacodynamic and pharmacokinetic properties, and therapeuticefficacy in the management of hypertension and angina pectoris. Drugs.1997 November; 54(5):774-93. Review), but it was removed from the marketdue to its severe interaction with other medicaments (Clozel J P, ErtelE A, Ertel S I; Voltage-gated T-type Ca2+ channels and heart failure.Proc Assoc Am Physicians. 1999 September-October; 111(5):429-37.Review). The EC50 of mibefradil on cells is between 0.1 and 1 μM,depending on the cell system (Martin et al., 2000, see above).Mibefradil however has an almost identical effect on both T-typeisotypes CaV3.1 und CaV3.3. The other blocker nickel has a 70 timeshigher EC50 on CaV3.2 than on the other isotypes (approx. 10 μM onCaV3.2 and 216 μM CaV3.3 and 25.0 μM on CaV3.3). Nickel, however, iscytotoxic so that it is only restrictedly suitable for pharmacologicanalyses of living tissue and is even unsuitable for medicamentous use.

The use of the skin-nerve preparation, which the present invention isbased on, allows for the electrophysiological analysis of the differentneurofibre types which innervate the skin (Koltzenburg et al., 1997, seeabove). The saphenous nerve and the region of the skin that itinnervates are prepared from freshly killed mice and are mounted in abath of physiological buffer. After mechanical or electrical stimulationof the skin, the nerve signals can be received directly from the nerve.For determining the effective concentration, tests were carried out withdifferent concentrations of mibefradil in the bath solution. The EC50 ofmibefradil on cells is between 0.1 and 1 μM. At high concentrations ofmore than 25 μM mibefradil in the bath solution, there was an almostcomplete and unspecific blocking of the mechanical sensitivity. If theconcentration was lowered to 3 μM, D-hair mechanoreceptors and, in part,also AM mechanoreceptors are specifically inhibited, the A-β fibres,however, not. The unspecific blockade at high concentrations may be dueto the fact that mibefradil, at high concentrations, has a veryunspecific effect on other ubiquitously expressed calcium channels. Suchblocking is lost at lower concentrations. The blocking of some AMmechanoreceptors also at low concentrations of mibefradil could have tworeasons. The first possibility is that AM mechanoreceptors, too, expressCaV3.2. This, however, is not very likely based on the findings obtainedby the in-situ hybridisation within the framework of the presentinvention. It may rather be assumed that a different isotype, i.e.CaV3.3 is expressed in AM mechanoreceptors. It was not possible todetect CaV3.3 in in-situ hybridisation experiments in spinal ganglia,but other groups reported the expression of this calcium channel inmedium-size cells. And it has been known that the semi-effectiveconcentration of mibefradil on CaV3.3 is almost identical to the one onCaV3.2. To sum up, it is concluded that the calcium channel CaV3.2 inspinal ganglia specifically expresses in D-hair mechanoreceptors and istherefore indispensable for its function. The discovery that thevoltage-dependent calcium channels are involved in the transduction ofmechanical stimuli by nociceptive and non-nociceptive neurons is new.Due to their physiological properties together with their specificlocalisation on the site of the mechanotransduction in the periphery,the calcium channels are ideal targets for pain therapy, which theinvention is based on.

Functional Model

It is not very likely that this T-type calcium channel is themechanosensitive ion channel that is responsible for the generation ofthe receptor potential. It is rather concluded that this calcium channelis a kind of signal enhancer. Moderately strong depolarisations whichare triggered by soft mechanical stimuli do normally not surpass thethreshold for the initiation of an action potential. It would bepossible to achieve a signal enhancement by inserting an ion channelwhich is activated even at low voltages. This would be a simpleexplanation for the high sensitivity of D-hair mechanoreceptors. CaV3.2has ideal prerequisites for fulfilling such a task as it is activatedeven at low voltages. Another feature of the D-hair receptors is theirfast adaptation, i.e. they are only active at the beginning and at theend of a mechanical stimulus, i.e. they are acceleration receptors. Aproperty of the CaV3.2 receptor is that it deactivates if these arestimuli in rapid succession, which is well compatible with thefast-adapting property of D-hair receptors.

Therapeutic Approach

The experiments of the invention were carried out on mice. Human CaV3.2shows a very high genetic homology and is very likely to exert similarfunctions. The new findings that the use of a calcium channel blocker(e.g. with mibefradil even at low concentrations (25 μM or less))virtually inhibits the entire cutaneous mechanotransduction, is ofparticular significance in the treatment of allodynia. These arepathological conditions in which the person perceives soft mechanicalstimuli on the skin, which are normally merely perceived as soft touchor tickling, as pain. This is most probably due to a change in theneuronal connections in the spinal cord.

A blockade of the mechanical sensitivity of the skin by the systemic ortopic addition of calcium channel blockers such as mibefradil is ofgreat clinical significance in terms of the treatment of suchconditions.

Extension of the Possibilities of Application

The data of the invention primarily relate to the calcium channelCaV3.2, a sub-type of the voltage-dependent calcium channels. It should,however, be noted that the blockade of other voltage-dependent calciumchannels can also be used for the treatment of the cited pain. It hasbeen found that the use of higher concentrations of mibefradil resultedin the complex blocking of other mechanoreceptors which have othercalcium channels. The group of voltage-dependent calcium channels can beclassified as follows:

As a result, at higher concentrations, mibefradil blocks not only theD-hair mechanotransduction but also the entire mechanotransduction. Thisis probably due to a blocking of other voltage-dependent calciumchannels, in particular the L- and N-type. N-type calcium channels areexpressed in all sensory neurons, whereas the L-type is mainly expressedin small cells (Scroggs R S, Fox A P; Calcium current variation betweenacutely isolated adult rat dorsal root ganglion neurons of differentsize. J. Physiol. 1992 January; 445:639-58) and are blocked bymibefradil at higher concentrations (about 10-fold higher than necessaryfor T-type blocking) (Mehrke G, Zong X G, Flockerzi V, Hofmann F. TheCa(++)-channel blocker Ro 40-5967 blocks different T-type and L-typeCa++channels. J Pharmacol Exp Ther. 1994 December;271(3):1483-8). Thisis why also dihydropyridines, the more effective L-type blockers, can beused for the treatment of the mentioned conditions of pain.Dihydropyridines have already been used clinically, e.g. for thetreatment of hypertension (Reuter H, Porzig H, Kokubun S, Prod'hom B.;Calcium channels in the heart. Properties and modulation bydihydropyridine enantiomers. Ann N Y Acad. Sci. 1988; 522:16-24.Review).

1. Pharmaceutical composition for the treatment of acute and/or chronicpain comprising calcium channel blockers that are capable of blockingvoltage-dependent calcium channels.
 2. Pharmaceutical composition asdefined in claim 1 wherein the calcium channel is a T-type or L-typechannel.
 3. Pharmaceutical composition as defined in claim 1 for thetreatment of allodynia or hyperalgesia.
 4. Pharmaceutical compositionaccording to claim 1 wherein the calcium channel blocker is mibefradil,its pharmaceutically acceptable analogues, salts or esters or adihydropyridine.
 5. Pharmaceutical composition according to claim 1 forthe treatment of pain associated with rheumatoid arthritis, cancer,injuries, back pain, herpes zoster and post-operative pain. 6.Pharmaceutical composition according to claim 1 for the topical, oral,parenteral, inhalative or intranasal administration.
 7. Pharmaceuticalcomposition according to claim 6 in form of an ointment, gel, creme or asolution or suspension, or plaster.
 8. Pharmaceutical compositionaccording to claim 6 in form of a nasal spray or inhalator.
 9. Methodfor the systemic therapy of pain, comprising administering apharmaceutical composition comprising calcium channel blockers that arecapable of blocking voltage-dependent calcium channels. 10.Pharmaceutical composition according to claim 1 wherein the compositionis in a drug form for oral administration, wherein the form is selectedfrom the group consisting of a tablet, a capsule, a coated tablet, agranulate, a juice, a syrup, a suspension, and a solution. 11.Pharmaceutical composition according to claim 1 wherein the drug formcomprises biologically utilizable or biodegradable substances selectedfrom the group consisting of proteins or proteides, lipids or lipoids,carbohydrates, polysaccharides and mixtures thereof.
 12. Pharmaceuticalcomposition according to claim 1 which further comprises one other painkiller.
 13. Pharmaceutical composition according to claim 12 wherein theother pain killer is selected from the group consisting of an NSAID, a5HT_(1D) agonist, a dopamin D₂ receptor antagonist, a secale alcaloid, abeta blocker, a calcium channel blocker, and a neurokinin antagonist.14. Pharmaceutical composition according to claim 12 wherein the NSAIDis ibuprofen, meoxicam, indomethacin or naporxen.
 15. Pharmaceuticalcomposition according to claim 12 wherein the 5HT_(1D) agonist issumatriptan, MK-452, naratriptan or 311C.
 16. Pharmaceutical compositionaccording to claim 12 wherein the dopamin D₂ receptor antagonist ismetoclopramid.
 17. Pharmaceutical composition according to claim 12wherein the secale alcaloid is ergotamin, dihydroergotamin ormetergolin.
 18. Pharmaceutical composition according to claim 12 whereinthe beta blocker is propranolol or metoprolol.
 19. Pharmaceuticalcomposition according to claim 12 wherein the calcium channel blocker isflunarizin or lomerizin.
 20. Pharmaceutical composition according toclaim 12 wherein the other pain killer is selected from the groupconsisting of acetylsalicylic acid, paracetamol, clonidin, methysergid,dotarizin, lisurid, pizotifen, valproat, aminotraptilin CP-122,288, andUK 116,044.